13C Natural Abundance in Serum Retinol Acts as a Biomarker for Increases in Dietary Provitamin A

The natural isotopic composition of C-13 and C-12 in tissues is largely determined by the diet. Sources of provitamin A carotenoids (e.g., vegetables) typically have a lower C-13 to C-12 ratio (C-13:C-12) than preformed vitamin A sources (i.e., dairy and meat) from corn-fed animals, which are prevalent in the US. The C-13:C-12 of serum retinol (C-13:C-12-retinol) was evaluated as a biomarker for vegetable intake in a 3-mo dietary intervention designed to promote weight-loss by increased vegetable consumption or reduced calorie and fat intake. Subjects were 21-50 y of age with a BMI between 30-40 kg/m(2) and were enrolled from one geographic area in the US. The high vegetable group (n = 20) was encouraged to increase daily vegetable and fruit consumption to 0.95 liter vegetables and 0.24-0.35 liter fruits. The caloric reduction group (n = 17) was encouraged to lower caloric intake by 500 kcal and consume <= 25% kcal from fat daily. Provided meals supplied 75-100% vegetable and fruit goals and 50-67% kcal and fat g per day. Carotenoid supplementation was discontinued by subjects during the study. Serum retinol and provitamin A carotenoid concentrations, intake of preformed vitamin A, provitamin A, and fat; and body weight, fat mass, and lean mass were analyzed for correlations to C-13:C-12-retinol. C-13:C-12-Retinol decreased in the vegetable group after intervention (P = 0.050) and the correlation with provitamin A intake was approaching significance (P = 0.079). C-13:C-12-Retinol did not change in the caloric reduction group (P = 0.43). C-13:C-12-Retinol changes with the vitamin A source in the diet and can be used as a biomarker for increases in dietary provitamin A vegetable intake. Exp Biol Med 234:140-147, 2009